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Infection with Clonorchis liver flukes arises from the ingestion of raw or poorly cooked fish contaminated by these parasites. After ingestion, these liver flukes grow to adulthood inside the human biliary duct system. Infections are not known to persist beyond 25–30 years, the lifespan of the parasite.

Diagnosis

Ova and parasite (O&P) stool examinations for liver fluke eggs is the only test available for the diagnosis of Clonorchis infection. More than one stool sample may be needed to identify the eggs. The eggs of Clonorchis are very similar to those of Opisthorchis, another liver fluke, but can be distinguished by microscopic features. Stool examination is unlikely to result in a diagnosis in persons whose only exposure to Clonorchis took place more than 25–30 years ago (the life span of a liver fluke), as the liver fluke must be living in order to produce eggs. Additionally, cysts containing the parasite can sometimes be detected by ultrasound, CT, or MRI. Serologic testing for Clonorchis is not useful for patient management and is not available in the United States. In the absence of detection of liver flukes, there is no test available that can determine if liver fluke infection is the underlying cause of cholangiocarcinoma or other hepatobiliary conditions. Routine screening of asymptomatic individuals with a history of travel to endemic countries for liver fluke infection is not recommended.

Risk for Cholangiocarcinoma

There are several parasites that cause liver fluke infections, including Fasciola, Clonorchis, and Opisthorchis. Among these, Fasciola infection is not associated with liver cancer. However, Clonorchis and Opisthorchis, two other liver flukes, are associated with liver cancer, specifically cholangiocarcinoma. Cholangiocarcinoma (CCA) is a rare cancer of the biliary duct system, which is comprised of the gallbladder and bile ducts. Only a small percentage of persons infected with Clonorchis or Opisthorchis develop complications such as cholangiocarcinoma. There are multiple non-parasitic risk factors for CCA, and liver fluke infections are very rarely associated with cases of CCA in the United States. Approximately 90% of patients diagnosed with cholangiocarcinoma in Western countries do not have a recognized risk factor.

Treatment

Praziquantel, adults, 75mg/kg/day orally, three doses per day for 2 days; the pediatric dosage is the same. Praziquantel should be taken with liquids during meals.

Alternative:

Albendazole* is an alternative drug; the dosage for adults is 10mg/kg/day for 7 days. The pediatric dosage is the same. Albendazole should be taken with food; a fatty meal increases the bioavailability.

*Not FDA-approved for this indication

Oral praziquantel is available for human use in the United States.

Oral albendazole is available for human use in the United States.

This information is provided as an informational resource for licensed health care providers as guidance only. It is not intended as a substitute for professional judgment.

Praziquantel

Praziquantel is pregnancy category B. There are no adequate and well-controlled studies in pregnant women. However, the available evidence suggests no difference in adverse birth outcomes in the children of women who were accidentally treated with praziquantel during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. For individual patients in clinical settings, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Praziquantel is excreted in low concentrations in human milk. According to WHO guidelines for mass prevention campaigns, the use of praziquantel during lactation is encouraged. For individual patients in clinical settings, praziquantel should be used in breast-feeding women only when the risk to the infant is outweighed by the risk of disease progress in the mother in the absence of treatment.

The safety of praziquantel in children aged less than 4 years has not been established. Many children younger than 4 years old have been treated without reported adverse effects in mass prevention campaigns and in studies of schistosomiasis. For individual patients in clinical settings, the risk of treatment of children younger than 4 years old who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Albendazole

Albendazole is pregnancy category C. Data on the use of albendazole in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated with albendazole during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of albendazole in the 2nd and 3rd trimesters of pregnancy. However, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

It is not known whether albendazole is excreted in human milk. Albendazole should be used with caution in breastfeeding women.

The safety of albendazole in children less than 6 years old is not certain. Studies of the use of albendazole in children as young as one year old suggest that its use is safe. According to WHO guidelines for mass prevention campaigns, albendazole can be used in children as young as 1 year old. Many children less than 6 years old have been treated in these campaigns with albendazole, albeit at a reduced dose.

Page last reviewed: May 20, 2020

Content source: Global Health, Division of Parasitic Diseases and Malaria